To determine the nature of biochemical lesions provoked by D- arabinosyl nucleosides and to exacerbate the cellular toxicity of these agents. a. Metabolism of D-arabinosyl adenine and araAMP. b. Metabolism of D-arabinosyl cytosine. To study the mechanism of increased lethality provoked by ara nucleotides, notably araAMP: a. Penetrability and incorporation of araAMP in mouse fibroblasts. b. Facilitation of nucleotide penetrability by derivatization and microencapsulation. c. The possible penetrability of other analogues of adenine nucleotides. d. The effects of ara nucleotides on mouse tumors. To study penetrability of sugar phosphates and their effect on animal cells. To study the penetration of animal cells by tRNA. To study the effect of S-adenosylmethionine analogues (including ara) on the metabolism of polyamines and nucleic acids. To study the utilization and effects of polyamine analogues, including ethidium and derivatives, on the metabolism of polyamines and nucleic acids. These studies will be carried out on mammalian and chick cells grown in tissue cultures. We will eventually extend such studies to cells infected by viruses, including tumor viruses.